Method of forming fine patterns

ABSTRACT

It is disclosed a method of forming fine patterns comprising: subjecting a substrate having photoresist patterns to a hydrophilic treatment, covering the substrate having photoresist patterns with an over-coating agent for forming fine patterns, applying heat treatment to cause thermal shrinkage of the over-coating agent so that the spacing between adjacent photoresist patterns is lessened by the resulting thermal shrinking action, and removing the over-coating agent substantially completely.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of forming fine patterns in the fieldof photolithographic technology. More particularly, the inventionrelates to a method of forming or defining fine patterns, such as holepatterns and trench patterns, that can meet today's requirements forhigher packing densities and smaller sizes of semiconductor devices.

2. Description of the Related Art

In the manufacture of electronic components such as semiconductordevices and liquid-crystal devices, there is employed thephotolithographic technology which, in order to perform a treatment suchas etching on the substrate, first forms a film (photoresist layer) overthe substrate using a so-called radiation-sensitive photoresist which issensitive to activating radiations, then performs exposure of the filmby selective illumination with an activating radiation, performsdevelopment to dissolve away the photoresist layer selectively to forman image pattern (photoresist pattern), and forms a variety of patternsincluding contact providing patterns such as a hole pattern and a trenchpattern using the photoresist pattern as a protective layer (maskpattern).

With the recent increase in the need for higher packing densities andsmaller sizes of semiconductor devices, increasing efforts are beingmade to form sufficiently fine-line patterns and submicron-electronicfabrication capable of forming patterns with linewidths of no more than0.20 μm is currently required. As for the activating light raysnecessary in the formation of mask patterns, short-wavelength radiationssuch as KrF, ArF and F₂ excimer laser beams and electron beams areemployed. Further, active R&D efforts are being made to find photoresistmaterials as mask pattern formers that have physical properties adaptedto those short-wavelength radiations.

In addition to those approaches for realizing submicron-electronicfabrication which are based on photoresist materials, active R&D effortsare also being made on the basis of pattern forming method with a viewto finding a technology that can provide higher resolutions than thosepossessed by photoresist materials.

For example, JP-5-166717A discloses a method of forming fine patternswhich comprises the steps of defining patterns (=photoresist-uncoveredpatterns) into a pattern-forming resist on a substrate, then coatingover entirely the substrate with a mixing generating resist that is tobe mixed with said pattern-forming resist, baking the assembly to form amixing layer on both sidewalls and the top of the pattern-formingresist, and removing the non-mixing portions of said mixing generatingresist such that the feature size of the photoresist-uncovered patternis reduced by an amount comparable to the dimension of said mixinglayer. JP-5-241348 discloses a pattern forming method comprising thesteps of depositing a resin, which becomes insoluble in the presence ofan acid, on a substrate having formed thereon a resist patterncontaining an acid generator, heat treating the assembly so that theacid is diffused from the resist pattern into said resin insoluble inthe presence of an acid to form a given thickness of insolubilizedportion of the resist near the interface between the resin and theresist pattern, and developing the resist to remove the resin portionthrough which no acid has been diffused, thereby ensuring that thefeature size of the pattern is reduced by an amount comparable to thedimension of said given thickness.

However, in these methods, it is difficult to control the thickness oflayers to be formed on the sidewalls of resist patterns. In addition,the in-plane heat dependency of wafers is as great as ten-odd nanometersper degree Celsius, so it is extremely difficult to keep the in-planeuniformity of wafers by means of the heater employed in currentfabrication of semiconductor devices and this leads to the problem ofoccurrence of significant variations in pattern dimensions.

Another approach known to be capable of reducing pattern dimensions isby fluidizing resist patterns through heat treatment and the like. Forexample, JP-1-307228A discloses a method comprising the steps of forminga resist pattern on a substrate and applying heat treatment to deformthe cross-sectional shape of the resist pattern, thereby defining a finepattern. In addition, JP-4-364021A discloses a method comprising thesteps of forming a resist pattern and heating it to fluidize the resistpattern, thereby changing the dimensions of its resist pattern to formor define a fine-line pattern.

In these methods, the wafer's in-plane heat dependency is only a fewnanometers per degree Celsius and is not very problematic. On the otherhand, it is difficult to control the resist deformation and fluidizingon account of heat treatment, so it is not easy to provide a uniformresist pattern in a wafer's plane.

An evolved version of those methods is disclosed in JP-7-45510A and itcomprises the steps of forming a resist pattern on a substrate, forminga stopper resin on the substrate to prevent excessive thermal fluidizingof the resist pattern, then applying heat treatment to fluidize theresist so as to change the dimensions of its pattern, and thereafterremoving the stopper resin to form or define a fine-line pattern. As thestopper resin, a water-soluble resin, specifically, polyvinyl alcohol isemployed singly. However, the use of polyvinyl alcohol singly is nothighly soluble in water and cannot be readily removed completely bywashing with water, introducing difficulty in forming a pattern of goodprofile. The pattern formed is not completely satisfactory in terms ofstability over time. In addition, polyvinyl alcohol cannot be appliedefficiently by coating. Because of these and other problems, the methoddisclosed in JP-7-45510 has yet to be adopted commercially.

Furthermore, in those traditional methods, as hydrophilic resins arecoated to form resin layers on the top or on the side walls of thephotoresist patterns that are being hydrophobic, it sometimes causesdifficulties in coating of the hydrophilic resins uniformly. Inaddition, with the recent tendency of wafers become. larger indiameters, the requirements for the formation of fine patterns becomeshighly difficulties, and the reduction of the usage amounts ofhydrophilic resins in forming the patterns is also required.Specifically, with the increase in the need of forming ultra finepatterns, it becomes difficult to apply the resins completely into onthe portions of the substrate between the photoresist patterns: thereare some portions whereto the resins cannot be applied into, andmicrofoaming occur, thereby to cause defectives in the formation of thepatterns.

JP 2001-281886A discloses a method comprising the steps of covering asurface of a resist pattern with an acidic film made of a resist patternsize reducing material containing a water-soluble resin, rendering thesurface layer of the resist pattern alkali-soluble, then removing saidsurface layer and the acidic film with an alkaline solution to reducethe feature size of the resist pattern. JP-2002-184673A discloses amethod comprising the steps of forming a resist pattern on a substrate,then forming a film containing a water-soluble film forming component onsaid resist pattern, heat treating said resist pattern and film, andimmersing the assembly in an aqueous solution of tetramethylammoniumhydroxide, thereby forming a fine-line resist pattern without involvinga dry etching step. However, both methods are simply directed toreducing the size of resist trace patterns themselves and therefore aretotally different from the present invention in object.

SUMMARY OF THE INVENTION

The present invention has been accomplished under these circumstancesand has as an object providing a method of forming fine patterns on asubstrate having photoresist patterns (mask patterns) as it is coveredwith an over-coating agent, in which having improvements in coatingproperties of the over-coating agent and coating uniformity, as well asthe reduction of the usage amounts of the over-coating agent.

In order to attain this object, the present invention provides a methodof forming fine patterns comprising: subjecting a substrate havingphotoresist patterns to a hydrophilic treatment, covering the substratehaving photoresist patterns with an over-coating agent for forming finepatterns, applying heat treatment to cause thermal shrinkage of theover-coating agent so that the spacing between adjacent photoresistpatterns is lessened by the resulting thermal shrinking action, andremoving the over-coating agent substantially completely.

In a preferred embodiment, the heat treatment is performed at atemperature that does not cause thermal fluidizing of the photoresistpatterns on the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The method of preparing the substrate used in the present inventionhaving photoresist patterns thereon is not limited to any particulartype and it can be prepared by conventional methods employed in thefabrication of semiconductor devices, liquid-crystal display devices,magnetic heads and microlens arrays. In an exemplary method, aphotoresist composition of chemically amplifiable or other type is spin-or otherwise coated on a substrate such as a silicon wafer and dried toform a photoresist layer, which is illuminated with an activatingradiation such as ultraviolet, deep-ultraviolet or excimer laser lightthrough a desired mask pattern using a reduction-projection exposuresystem or subjected to electron beam photolithography, then heated anddeveloped with a developer such as an alkaline aqueous solution,typically a 1-10 mass % tetramethylammonium hydroxide (TMAH) aqueoussolution, thereby forming a photoresist pattern on the substrate.

The photoresist composition serving as a material from which photoresistpatterns are formed is not limited in any particular way and any commonphotoresist compositions may be employed including those for exposure toi- or g-lines, those for exposure with an excimer laser (e.g. KrF, ArFor F₂) and those for exposure to EB (electron beams).

[a.] Substrate Hydrophilic Treatment Step

A substrate having photoresist patterns (mask patterns) thereon issubjected to a hydrophilic treatment. Any method can be used for thehydrophilic treatment so far as it can provide hydrophilicity to thesurfaces of the substrate and the photoresist patterns without producingno ill effects to them. More specifically, methods such as applying asmall amount of a hydrophilic solvent (an application improving agent)on the substrate, exposing the substrate in an atmosphere of steam,irradiating UV rays to the entire substrate, O₂ plasma ashing treatingto the substrate, and the like, are exemplified.

In the present invention, a method of applying a small amount of ahydrophilic solvent (an application improving agent) on the substrate ispreferred. As the hydrophilic solvent, pure water, a water-solublesurfactant aqueous solution, and an alcohol aqueous solution arepreferably used.

As water-soluble surfactants in the invention, at least the one selectedamong N-alkylpyrrolidones, quaternary ammonium salts and phosphateesters of polyoxyethylene are preferably employed, in view of theprovision of no ill effects to the substrate and the photoresistpatterns, and the most effectively exhibition of the advantages of thepresent invention. However, they are not limited thereto.

N-alkylpyrrolidones as surfactant are preferably represented by thefollowing general formula (I):

where R₁ is an alkyl group having at least 6 carbon atoms.

Specific examples of N-alkylpyrrolidones as surfactant includeN-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone andN-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone(“SURFADONE LP 100” of ISP Inc.) is preferably used.

Quaternary ammonium salts as surfactant are preferably represented bythe following general formula (II):

where R₂, R₃, R₄ and R₅ are each independently an alkyl group or ahydroxyalkyl group (provided that at least one of them is an alkyl orhydroxyalkyl group having not less than 6 carbon atoms); X⁻ is ahydroxide ion or a halogenide ion.

Specific examples of quaternary ammonium salts as surfactant includedodecyltrimethylammonium hydroxide, tridecyltrimethylammonium hydroxide,tetradecyltrimethylammonium hydroxide, pentadecyltrimethylammoniumhydroxide, hexadecyltrimethylammonium hydroxide,heptadecyltrimethylammonium hydroxide and octadecyltrimethylammoniumhydroxide. Among these, hexadecyltrimethylammonium hydroxide ispreferably used.

Phosphate esters of polyoxyethylene are preferably represented by thefollowing general formula (III):

where R₆ is an alkyl or alkylaryl group having 1-10 carbon atoms; R₇ isa hydrogen atom or (CH₂CH₂O)R₆ (where R₆ is as defined above): n is aninteger of 1-20.

To mention specific examples, phosphate esters of polyoxyethylene thatcan be used as surfactants are commercially available under trade names“PLYSURF A212E” and “PLYSURF A210G” from Dai-ichi Kogyo Seiyaku Co.,Ltd.

The water-soluble surfactants are preferably used by solving in purewater to obtain a water-soluble surfactant aqueous solution having apreferable concentration of 0.001-10 mass %, and more preferably 0.01-3mass %.

As the alcohol, a monohydric alcohol, such as methyl alcohol, ethylalcohol, propylene alcohol, and butyl alcohol; and a polyhydric alcohol,such as ethylene glycol, propylene glycol, and glycerol are exemplified,but are not limited thereto. The alcohols are preferably used by solvingin pure water to obtain an alcohol aqueous solution having a preferableconcentration of 0.01-30 mass %, and more preferably 0.1-20 mass %.

The coating amount of the hydrophilic solvent (an application improvingagent) can be the minimum amount so far as the solvent can be appliedentirely over the substrate having photoresist patterns thereon, and notlimited to any particular amounts. The preferable amount is about0.05-10 mL, and more preferably 0.1-3 mL for the coating on an 8-inchsilicon wafer. The solvent is generally applied on the substrate bywhirl coating with a spinner, but not limited thereto. In the case wherethe amount of the solvent for the application is too little, the effectsobtainable by the utilization of the hydrophilic solvent cannot beexhibited. On the other hand, in the case where the amount of thesolvent is too much, a takt time is liable to be longer.

[b.] Over-Coating Agent Application Step

In the next step, an over-coating agent is applied to cover entirely thesaid substrate having photoresist patterns (mask patterns) thereon. Inthe present invention, the over-coating agent application step isperformed after step [a.], the usage amount of the over-coating agentcould be reduced sharply. For example, in applying the over-coatingagent to an 8-inch silicon wafer, it was able to reduce the amount ofthe over-coating agent to 1-3 mL in the present invention, whereas in acommon applying method without including step [a.] where 4-6 mL of theover-coating coating was applied. Even the amount of the over-coatingagent could be reduced one half like this, the same coating uniformitywas obtained as that of in the common application method. Further, evenfor the substrate that have photoresist patterns having ultra-fine linesand being formed thickly thereon, the over-coating agent is easily andcompletely applied into on the portions of the substrate between suchphotoresist patterns without the occurrence of micrbfoaming. Theover-coating agent was applied in uniformity with efficiency.

After applying the over-coating agent, the substrate may optionally bepre-baked at a temperature of 80-100° C. for 30-90 seconds.

The over-coating agent may be applied by any methods commonly employedin the conventional heat flow process. Specifically, an aqueous solutionof the over-coating agent for forming fine patterns is applied to thesubstrate by any known application methods including bar coating, rollcoating and whirl coating with a spinner.

The over-coating agent employed in the invention is to cover entirelythe substrate having photoresist patterns (mask patterns) thereon,including patterns typified by hole patterns or trench patterns, each ofthese patterns are defined by spacing between adjacent photoresistpatterns (mask patterns). Upon heating, the applied film of over-coatingagent shrinks to increase the width of each of the photoresist patterns,thereby narrowing or lessening adjacent hole patterns or trench patternsas defined by spacing between the photoresist patterns and, thereafter,the applied film is removed substantially completely to form or definefine featured patterns.

The phrase “removing the applied film substantially completely” as usedherein means that after lessening the spacing between adjacentphotoresist patterns by the heat shrinking action of the appliedover-coating agent, said film is removed in such a way that nosignificant thickness of the over-coating agent will remain at theinterface with the photoresist patterns. Therefore, the presentinvention does not include methods in which a certain thickness of theover-coating agent is left intact near the interface with thephotoresist pattern so that the feature size of the pattern is reducedby an amount corresponding to the residual thickness of the over-coatingagent.

In the present invention, the over-coating agent is preferably employedthat contains a water-soluble polymer.

The water-soluble polymer may be any polymer that can dissolve in waterat room temperature and various types may be employed without particularlimitation; preferred examples include acrylic polymers, vinyl polymers,cellulosic derivatives, alkylene glycol polymers, urea polymers,melamine polymers, epoxy polymers and amide polymers.

Exemplary acrylic polymers include polymers and copolymers havingmonomeric components, such as acrylic acid, methyl acrylate, methacrylicacid, methyl methacrylate, N,N-dimethylacrylamide,N,N-dimethylaminopropylmethacrylamide,N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.

Exemplary vinyl polymers include polymers and copolymers havingmonomeric components, such as N-vinylpyrrolidone, vinyl imidazolidinone,vinyl acetate, etc.

Exemplary cellulosic derivatives include hydroxypropylmethyl cellulosephthalate, hydroxypropylmethyl cellulose acetate phthalate,hydroxypropylmethyl cellulose hexahydrophthalate, hydroxypropylmethylcellulose acetate succinate, hydroxypropylmethyl cellulose,hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetatehexahydrophthalate, carboxymethyl cellulose, ethyl cellulose,methylcellulose, etc.

Exemplary alkylene glycol polymers include addition polymers andcopolymers of ethylene glycol, propylene glycol, etc.

Exemplary urea polymers include those having methylolurea,dimethylolurea, ethyleneurea, etc. as components.

Exemplary melamine polymers include those having methoxymethylatedmelamine, methoxymethylated isobutoxymethylated melamine,methoxyethylated melamine, etc. as components.

Among epoxy polymers and amide polymers, those which are water-solublemay also be employed.

It is particularly preferred to employ at least one member selected fromthe group consisting of alkylene glycol polymers, cellulosicderivatives, vinyl polymers and acrylic polymers. Acrylic polymers aremost preferred since they provide ease in pH adjustment. Copolymerscomprising acrylic polymers and water-soluble polymers other thanacrylic polymers are also preferred since during heat treatment, theefficiency of shrinking the spacing between the adjacent photoresistpatterns (mask patterns) can be increased while maintaining the shape ofthe photoresist pattern. The water-soluble polymers can be employedeither singly or in combination.

When water-soluble polymers are used as copolymers, the proportions ofthe components are not limited to any particular values. However, ifstability over time is important, the proportion of the acrylic polymeris preferably adjusted to be larger than those of other buildingpolymers. Other than by using excessive amounts of the acrylic polymer,better stability over time can also be obtained by adding acidiccompounds such as p-toluenesulfonic acid and dodecylbenzenesulfonicacid.

The over-coating agent for forming fine patterns may additionallycontain water-soluble amines. Preferred ones include amines having pKa(acid dissociation constant) values of 7.5-13 in aqueous solution at 25°C. in view of the prevention of the generation of impurities and pHadjustment. Specific examples include the following: alkanolamines, suchas monoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine and triisopropanolamine:polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenediamine,1,4-butanediamine, N-ethylethylenediamine, 1,2-propanediamine,1,3-propanediamine and 1,6-hexanediamine; aliphatic amines, such astriethylamine, 2-ethyl-hexylamine, dioctylamine, tributylamine,tripropylamine, triallylamine, heptylamine and cyclohexylamine; aromaticamines, such as benzylamine and diphenylamine; and cyclic amines, suchas piperazine, N-methyl-piperazine and hydroxyethylpiperazine. Preferredwater-soluble amines are those having boiling points of 140° C. (760mmHg) and above, as exemplified by. monoethanolamine andtriethanolamine.

If the water-soluble amine is to be added, it is preferably incorporatedin an amount of about 0.1-30 mass %, more preferably about 2-15 mass %,of the over-coating agent (in terms of solids content). If thewater-soluble amine is incorporated in an amount of less than 0.1 mass%, the coating fluid may deteriorate over time. If the water-solubleamine is incorporated in an amount exceeding 30 mass %, the photoresistpattern being formed may deteriorate in shape.

The over-coating agent for forming fine patterns is adjusted to have pHvalues of 2-3 by the addition of the water-soluble amine. There may becases where the over-coating agent for forming fine patterns is appliedto the substrate having metallic layers easily corroded by an acid, thepH values may be adjusted to 3-5.

For such purposes as reducing the dimensions of patterns and controllingthe occurrence of defects, the over-coating agent for forming finepatterns may further optionally contain non-amine based, water-solubleorganic solvents.

As such non-amine based, water-soluble organic solvents, any non-aminebased organic solvents that can mix with water may be employed and theymay be exemplified by the following: sulfoxides, such as dimethylsulfoxide; sulfones, such as dimethylsulfone, diethylsulfone,bis(2-hydroxyethyl)sulfone and tetramethylenesulfone; amides, such asN,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide,N-methylacetamine and N,N-diethylacetamide; lactams, such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone and 1,3-diisopropyl-2-imidazolidinone; andpolyhydric alcohols and derivatives thereof, such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobuthyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobuthyl ether, propylene glycol, propylene glycolmonomethyl ether, glycerol, 1,2-butylene glycol, 1,3-butylene glycol and2,3-butylene glycol. Among those mentioned above, polyhydric alcoholsand their derivatives are preferred for the purposes of reducing thedimensions of patterns and controlling the occurrence of defects andglycerol is particularly preferred. The non-amine based, water-solubleorganic solvents may be used either singly or in combination.

If the non-amine based, water-soluble organic solvent is to be added, itis preferably incorporated in an amount of about 0.1-30 mass %, morepreferably about 0.5-15 mass %, of the water-soluble polymer. If thenon-amine based, water-soluble organic solvent is incorporated in anamount of less than 0.1 mass %, its defect reducing effect tends todecrease. Beyond 30 mass %, a mixing layer is liable to form at theinterface with the photoresist pattern.

In addition, the over-coating agent may optionally contain a surfactantfor attaining special effects such as coating uniformity and wafer'sin-plane uniformity.

The surfactant is preferably employed that, when added to thewater-soluble polymer, exhibits certain characteristics such as highsolubility, non-formation of a suspension and miscibility with thepolymer component. By using surfactants that satisfy thesecharacteristics, the occurrence of defects can be effectively controlledthat is considered to be pertinent to microfoaming upon coating theover-coating agent.

From the points above, surfactants in the invention are preferablyemployed at least the one selected among N-alkylpyrrolidones, quaternaryammonium salts and phosphate esters of polyoxyethylene, that are usedfor a hydrophilic solvent used in step [a.] above.

If the surfactant is to be added, it is preferably incorporated in anamount of about 0.1-10 mass %, more preferably about 0.2-2 mass %, ofthe over-coating agent (in terms of solids content). By adopting theamount as described above ranges, it may effectively prevent thevariations in the percent shrinkage of patterns, potentially dependingon the wafer's in-plane uniformity which is caused by the deteriorationof coating property, and also prevent the occurrence of defects that areconsidered to have cause-and-effect relations with microfoaming on theapplied film that generates as the coating conditions are worsened.

The over-coating agent of the invention for forming fine patterns ispreferably used as an aqueous solution at a concentration of 3-50 mass%, more preferably at 5-30 mass %. If the concentration of the aqueoussolution is less than 3 mass %, poor coverage of the substrate mayresult. If the concentration of the aqueous solution exceeds 50 mass %,there is no appreciable improvement in the intended effect thatjustifies the increased concentration and the solution cannot be handledefficiently.

As already mentioned, the over-coating agent in the invention forforming fine patterns is usually employed as an aqueous solution usingwater as the solvent. A mixed solvent system comprising water and analcoholic solvent may also be employed. Exemplary alcoholic solventsinclude methyl alcohol, ethyl alcohol, propyl alcohol, isopropylalcohol, glycerol, ethylene glycol, propylene glycol, 1,2-butyleneglycol, 1,3-buthylene glycol and 2,3-butylene glycol, etc. Thesealcoholic solvents are mixed with water in amounts not exceeding about30 mass %.

[c.] Heat Treatment (Thermal Shrinkage) Step

In the next step, heat treatment is performed to cause thermal shrinkageof the film of the over-coating agent. Under the resulting force ofthermal shrinkage of the film, the dimensions of the photoresist patternin contact with the film will increase by an amount equivalent to thethermal shrinkage of the film and, as the result, the photoresistpattern widens and accordingly the spacing between adjacent photoresistpatterns lessens. The spacing between adjacent photoresist patternsdetermines the diameter or width of the pattern elements to be finallyobtained, so the decrease in the spacing between adjacent photoresistpatterns contributes to reducing the diameter of each element of a holepattern or the width of each element of a trench pattern, eventuallyleading to the definition of a pattern with smaller feature sizes.

The heating temperature is not limited to any particular value as longas it is high enough to cause thermal shrinkage of the film of theover-coating agent and form or define a fine pattern. Heating ispreferably done at a temperature that will not cause thermal fluidizingof the photoresist pattern. The temperature that will not cause thermalfluidizing of the photoresist pattern is such a temperature that when asubstrate on which the photoresist pattern has been formed but no filmof the over-coating agent has been formed is heated, the photoresistpattern will not experience any dimensional changes. Performing a heattreatment under such temperature conditions is very effective forvarious reasons, e.g. a fine-line pattern of good profile can be formedmore efficiently and the duty ratio in the plane of a wafer, or thedependency on the spacing between photoresist patterns in the plane of awafer, can be reduced. Considering the softening points of a variety ofphotoresist compositions is employed in current photolithographictechniques, the preferred heat treatment is usually performed within atemperature range of about 80-160° C. for 30-90 seconds, provided thatthe temperature is not high enough to cause thermal fluidizing of thephotoresist.

The thickness of the film of the over-coating agent for the formation offine-line patterns is preferably just comparable to the height of thephotoresist pattern or high enough to cover it.

[d.] Over-Coating Agent Removal Step

In the subsequent step, the remaining film of the over-coating agent onthe patterns is removed by washing with an aqueous solvent, preferablypure water. Prior to washing with water, rinsing may optionally beperformed with an aqueous solution of alkali (e.g. tetramethylammoniumhydroxide (TMAH) or choline). The over-coating agent of the presentinvention is easy to remove by washing with water and it can becompletely removed from the substrate and the photoresist pattern. Thecontact method of the substrate with the aqueous solution can beperformed by, for example, a puddle method, a dip method, a showermethod, a spray method, etc., but is not limited thereto. The contacttime of the substrate with the aqueous solution is in usual for 10-300seconds, but is not limited thereto.

As a result, each pattern on the substrate has a smaller feature sizebecause each pattern is defined by the narrowed spacing between theadjacent widened photoresist patterns.

The fine-line pattern thus formed using the over-coating agent of thepresent invention has a pattern size smaller than the resolution limitattainable by the conventional methods. In addition, it has a goodenough profile and physical properties that can fully satisfy thecharacteristics required of semiconductor devices.

Steps [a.]-[d.] may be repeated several times. By repeating steps[a.]-[d.] several times, the photoresist trace patterns (mask patterns)can be progressively widened. Furthermore, the use of the over-coatingagent for forming fine patterns containing a water-soluble polymerallows the over-coating agent be completely removed with water everytime in repeating the removal step plural times. Therefore, the presentinvention offers the advantage that even in the case of using asubstrate having thick-film photoresist patterns, fine-line patterns ofgood profile can be formed on the substrate without causing patterndistortion or deformation.

Furthermore, the adopting a substrate hydrophilic treatment step priorto the coating step of the over-coating allows the application of theover-coating agent into on the portions of the substrate betweenphotoresist patterns easily and completely. Owing to this, the in-planeuniformity of the heat shrinkage of the over-coating agent was improved,and good profile patterns can be formed entirely across even on alarge-diameter substrate.

The technical field of the present invention is the semiconductorindustry, etc., but it is not limited thereto.

EXAMPLES

The following examples are provided for further illustrating the presentinvention but are in no way to be taken as limiting. Unless otherwisenoted, all amounts of ingredients are expressed in mass %.

Example 1

A copolymer including polyvinylpyrrolidone (PVP) polyacrylate (PAA)[6.37 g; NVP copolymer, NOF Corporation], triethanolamine (0.57 g) and apolyoxyethyelene phosphate ester surfactant (0.06 g; “PLYSURF A21OG”,product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were dissolved in water (93g) to prepare an over-coating agent.

A substrate (8-inch diameter) was whirl coated with a positive-actingphotoresist TDUR-P036PM (product of Tokyo Ohka Kogyo Co., Ltd.) andbaked at 80° C. for 90 seconds to form a photoresist layer in athickness of 0.48 μm.

The photoresist layer was exposed with an exposure unit (CanonFPA-3000EX3, product of Canon Inc.), subjected to heat treatment at 120°C. for 90 seconds and developed with an aqueous solution of 2.38 mass %TMAH (tetramethylammonium hydroxide) to form photoresist patterns whichdefined hole patterns with an each diameter of 180.2 nm (i.e., thespacing between the photoresist patterns, or the initial hole dimension,was 180.2 nm).

Next, pure water (2 mL) was applied onto the substrate for thehydrophilic treatment. After that, the previously prepared over-coatingagent (3 mL) was applied onto the substrate including hole patterns.There were no coating variations and a good coating uniformity wasobtained.

Then, the thusly treated substrate was subjected to heat treatment at116° C. for 60 seconds, thereby reducing the each size of the holepatterns. Subsequently, the substrate, while being kept whirling at 1500rpm, was brought into contact with pure water by dropping it on thesubstrate for 120 seconds to remove the over-coating agent. The eachdiameter of the hole patterns was reduced to 160.5 nm.

Example 2

A copolymer including polyvinylpyrrolidone (PVP) polyacrylate (PAA)[6.37 g; NVP copolymer, NOF Corporation], triethanolamine (0.57 g) and apolyoxyethyelene phosphate ester surfactant (0.06 g; “PLYSURF A210G”,product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were dissolved in water (93g) to prepare an over-coating agent.

Also, a polyoxyethyelene phosphate ester surfactant (0.1 g; “PLYSURFA210G”, product of Dai-ichi Kogyo Seiyaku Co, Ltd.) was dissolved inwater (99 g) to prepare a hydrophilic solvent (an application improvingagent).

A substrate (8-inch diameter) was whirl coated with a positive-actingphotoresist TDUR-P036PM (product of Tokyo Ohka Kogyo Co., Ltd.) andbaked at 80° C. for 90 seconds to form a photoresist layer in athickness of 0.48 μm.

The photoresist layer was exposed with an exposure unit (CanonFPA-3000EX3, product of Canon Inc.), subjected to heat treatment at 120°C. for 90 seconds and developed with an aqueous solution of 2.38 mass %TMAH (tetramethylammonium hydroxide) to form photoresist patterns whichdefined hole patterns with an each diameter of 180.2 nm (i.e., thespacing between the photoresist patterns, or the initial hole dimension,was 180.2 nm).

Next, the above-described hydrophilic solvent (the application improvingagent) (2 mL) was applied onto the substrate for the hydrophilictreatment. After that, the previously prepared over-coating agent (3 mL)was applied onto the substrate including hole patterns. There were nocoating variations and a good coating uniformity was obtained.

Then, the thusly treated substrate was subjected to heat treatment at116° C. for 60 seconds, thereby reducing the each size of the holepatterns. Subsequently, the substrate, while being kept whirling at 1500rpm, was brought into contact with pure water by dropping it on thesubstrate for 120 seconds to remove the over-coating agent. The eachdiameter of the hole patterns was reduced to 160.0 nm.

Comparative Example 1

The same procedure as described in Example 1 was repeated, except thatthe application step of pure water (an application improving agent) wasomitted. As a result, coating variations were occurred and the substratehaving the photoresist patterns thereon was not entirely covered withthe over-coating agent, and therefore the patterns partially could notbe lessened.

In addition, when the procedure of Comparative Example 1 was repeated,except that the amount of the over-coating agent was increased to double(6 mL), the coating variations did not occur.

As described above in detail, the present invention provide a method forforming fine patterns, by which advantages obtained of improving coatingproperties of the over-coating agent and uniformity of the filmthickness, as well as reducing the usage amount of the over-coatingagent.

1. A method of forming fine patterns comprising: subjecting a substratehaving photoresist patterns to a hydrophilic treatment, covering thesubstrate having photoresist patterns with an over-coating agent forforming fine patterns, applying heat treatment to cause thermalshrinkage of the over-coating agent so that the spacing between adjacentphotoresist patterns is lessened by the resulting thermal shrinkingaction, and removing the over-coating agent substantially completely. 2.The method of forming fine patterns according to claim 1, wherein thehydrophilic treatment is performed by applying a hydrophilic solvent onthe substrate having photoresist patterns.
 3. The method of forming finepatterns according to claim 2, wherein the hydrophilic solvent is atleast one member selected from the group consisting of pure water, awater-soluble surfactant aqueous solution, and an alcohol aqueoussolution.
 4. The method of forming fine patterns according to claim 3,wherein the hydrophilic solvent is pure water.
 5. The method of formingfine patterns according to claim 1, wherein the over-coating agentcontains a water-soluble polymer.
 6. The method of forming fine patternsaccording to claim 5, wherein the water-soluble polymer is at least onemember selected from the group consisting of alkylene glycolic polymers,cellulosic derivatives, vinyl polymers, acrylic polymers, urea polymers,epoxy polymers, melamine polymers and amide polymers.
 7. The method offorming fine patterns according to claim 1, wherein the over-coatingagent is an aqueous solution having a solids content of 3-50 mass %. 8.The method of forming fine patterns according to claim 1, wherein theheat treatment is performed at a temperature that does not cause thermalfluidizing of the photoresist patterns on the substrate.